A sungrazing comet is a comet that passes extremely close to the Sun at perihelion – sometimes within a few thousand kilometres of the Sun's surface. While small sungrazers can be completely evaporated during such a close approach to the Sun, larger sungrazers can survive many perihelion passages. However, the strong evaporation and tidal forces they experience often lead to their fragmentation.
The Kreutz Sungrazers
The most famous sungrazers are the Kreutz Sungrazers, which all originate from one giant comet that broke up into many smaller comets during its first passage through the inner Solar System. An extremely bright comet seen by Aristotle and Ephorus in 371 BC is a possible candidate for this parent comet.
The Great Comets of 1843 and 1882, Comet Ikeya–Seki in 1965 and C/2011 W3 (Lovejoy) in 2011 were all fragments of the original comet. Each of these three was briefly bright enough to be visible in the daytime sky, next to the Sun, outshining even the full moon.
Since the launch of the SOHO satellite in 1995, hundreds of tiny Kreutz Sungrazers have been discovered, all of which have either plunged into the Sun or been destroyed completely during their perihelion passage, with the exception of C/2011 W3 (Lovejoy). The Kreutz family of comets is apparently much larger than previously suspected.
About 83% of the sungrazers observed with SOHO are members of the Kreutz group. The other 17% contains some sporadic sungrazers, but three other related groups of comets have been identified among them: the Kracht, Marsden and Meyer groups. The Marsden and Kracht groups both appear to be related to Comet 96P/Machholz. These comets have also be linked to several meteor streams, including the Daytime Arietids, the delta Aquariids, and the Quadrantids. Linked comet orbits suggest that both Marsden and Kracht groups have a small period, on the order of five years, but the Meyer group may have intermediate- or long-period orbits. The Meyer group comets are typically small, faint, and never have tails. The Great Comet of 1680 was a sungrazer and while used by Newton to verify Kepler's equations on orbital motion, it was not a member of any larger groups. However, comet C/2012 S1 (ISON) has orbital elements similar to the Great Comet of 1680 and could be a second member of the group.
Origin of sungrazing comets
Studies show that for comets with high orbital inclinations and perihelion distances of less than about 2 astronomical units, the cumulative effect of gravitational perturbations over many orbits is adequate to reduce the perihelion distance to very small values. One study has suggested that Comet Hale–Bopp has about a 15% chance of eventually becoming a sungrazer.
Role in solar astronomy
The motion of tails of sungrazers that survive perihelion (such as Comet Lovejoy) can provide solar astronomers with information about the structure of the solar corona, particularly the detailed magnetic structure. 
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